bpf: Rewrite any fault prone load out of a mem or btf_id pointer

bpf_convert_ctx_accesses() turns a BPF_LDX into a BPF_PROBE_MEM one by
matching the type recorded for the insn against a list of exact pointer
types. The list cannot keep up with the flag combinations the verifier
produces, and a type which is missing from it ends up as a plain load
without an exception table entry, so a bad address panics the kernel
instead of being handled.

Two such types exist today and are reachable:

  - PTR_TO_BTF_ID | PTR_UNTRUSTED | MEM_ALLOC | NON_OWN_REF
  - PTR_TO_BTF_ID | PTR_UNTRUSTED | MEM_RCU

Rather than adding the two, just drop the list and state the property
itself in the default case of the switch. This is a superset of what
the list matched, the untrusted PTR_TO_MEM does not have to carry
MEM_RDONLY for it anymore, and it stays in sync with the verifier side
which uses the same match in save_aux_ptr_type() and reg_type_mismatch_ok().

Assert that a fault prone type which does not get the rewrite for whatever
reason is rejected at load time rather than left to fault at runtime to
catch any future cases.

Fixes: 1b12171533a9 ("bpf: Mark direct ld of stashed bpf_{rb,list}_node as non-owning ref")
Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260814215301.709827-4-daniel@iogearbox.net

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index ae0274a4bf35..5fad59fdab0d 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1308,6 +1308,17 @@ static inline u32 type_flag(u32 type)
 	return type & ~BPF_BASE_TYPE_MASK;
 }
 
+static inline bool bpf_is_ptr_to_mem_or_btf_id(enum bpf_reg_type type)
+{
+	switch (base_type(type)) {
+	case PTR_TO_MEM:
+	case PTR_TO_BTF_ID:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static inline bool bpf_may_fault_on_deref(enum bpf_reg_type type)
 {
 	/*